Lethal Mutations and Cell Death

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Abstract
From observations on the interaction of modifying treatments, it has been inferred that death of bacteria may result from at least two different types of event initiated by radiation, the involvement of oxygen in these events being intrinsically different. It has been concluded that one type of damage, referred to as ` type N ', has a rather low associated oxygen enhancement ratio; and comparisons of the effects of various modifying treatments on mutation induction and on cell death have suggested that radiation death resulting from type N damage is akin to the induction of lethal mutations; but death may also result from ` type O ' damage which is associated with a considerably higher oxygen enhancement ratio. The magnitude of the contribution by lethal mutations, i.e. by ` type N ' damage, to the overall bactericidal effect of radiation depends on the biochemical characteristics of the strain under test as well as on conditions during irradiation and culture conditions afterwards. While much less evidence is available on the modification of the cytocidal effects of radiation on higher cells, there is sufficient to suggest that (a) the causal relationship of cell death to gross chromosomal damage may be only a rough approximation, (b) the induction of chromosome damage by ionizing radiation may be due to more than one type of initiating event, with more than one associated oxygen enhancement ratio.